Fumarates suppress Th1 responses by blocking IL-12 and IL-23 production by dendritic cells via distinct pathways.

Peroxisome proliferator-activated receptors (PPAR) are members of a nuclear hormone receptor superfamily that includes receptors for steroids, retinoids, and thyroid hormone, all of which are known to affect the immune response. Previous studies dealing with PPAR-γ expression in the immune system have been limited. Recently, PPAR-γ was identified in monocyte/macrophage cells. In this study we examined the role of PPAR-γ in experimental autoimmune encephalomyelitis (EAE), an animal model for the human disease multiple sclerosis. The hypothesis we are testing is whether PPAR-γ plays an important role in EAE pathogenesis and whether PPAR-γ ligands can inhibit the clinical expression of EAE. Initial studies have shown that the presence of the PPAR-γ ligand 15-deoxy-Δ12,14-PGJ2 (15d-PGJ2) inhibits the proliferation of Ag-specific T cells from the spleen of myelin basic protein Ac1–11 TCR-transgenic mice. 15d-PGJ2 suppressed IFN-γ, ΙL-10, and IL-4 production by both Con A- and myelin basic protein Ac1–11 peptide-stimulated lymphocytes as determined by ELISA and ELISPOT assay. Culture of encephalitogenic T cells with 15d-PGJ2 in the presence of Ag reduced the ability of these cells to adoptively transfer EAE. Examination of the target organ, the CNS, during the course of EAE revealed expression of PPAR-γ in the spinal cord inflammatory infiltrate. Administration of 15d-PGJ2 before and at the onset of clinical signs of EAE significantly reduced the severity of disease. These results suggest that PPAR-γ ligands may be a novel therapeutic agent for diseases such as multiple sclerosis.

IL-17-producing T cells (Th17) have recently been implicated in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an animal model for the human disease multiple sclerosis. However, little is known about the transcription factors that regulate these cells. Although it is clear that the transcription factor T-bet plays an essential role in the differentiation of IFN-γ-producing CD4+ Th1 lymphocytes, the potential role of T-bet in the differentiation of Th17 cells is not completely understood. In this study, therapeutic administration of a small interfering RNA specific for T-bet significantly improved the clinical course of established EAE. The improved clinical course was associated with suppression of newly differentiated T cells that express IL-17 in the CNS as well as suppression of myelin basic protein-specific Th1 autoreactive T cells. Moreover, T-bet was found to directly regulate transcription of the IL-23R, and, in doing so, influenced the fate of Th17 cells, which depend on optimal IL-23 production for survival. We now show for the first time that suppression of T-bet ameliorates EAE by limiting the differentiation of autoreactive Th1 cells, as well as inhibiting pathogenic Th17 cells via regulation of IL-23R.

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily. PPARγ ligands, which include the naturally occurring PG metabolite 15-deoxy-Δ12,14-PGJ2 (15d-PGJ2), as well as thiazolidinediones, have been shown to have anti-inflammatory activity. The PPARα agonists, gemfibrozil, ciprofibrate, and fenofibrate, have an excellent track history as oral agents used to treat hypertriglyceridemia. In the present study, we demonstrate that these PPARα agonists can increase the production of the Th2 cytokine, IL-4, and suppress proliferation by TCR transgenic T cells specific for the myelin basic protein Ac1–11, as well as reduce NO production by microglia. Oral administration of gemfibrozil and fenofibrate inhibited clinical signs of experimental autoimmune encephalomyelitis. More importantly, gemfibrozil was shown to shift the cytokine secretion of human T cell lines by inhibiting IFN-γ and promoting IL-4 secretion. These results suggest that PPARα agonists such as gemfibrozil and fenofibrate, may be attractive candidates for use in human inflammatory conditions such as multiple sclerosis.

As a means of developing therapies that target the pathogenic T cells in multiple sclerosis (MS) without compromising the immune system or eliciting systemic side effects, we investigated the use of T-bet-specific antisense oligonucleotides and small interfering RNAs (siRNA) to silence T-bet expression in autoreactive encephalitogenic T cells and evaluated the biological consequences of this suppression in experimental autoimmune encephalomyelitis, a model for MS. The T-bet-specific AS oligonucleotide and siRNA suppressed T-bet expression, IFNgamma production, and STAT1 levels during antigen-specific T cell differentiation. In vitro suppression of T-bet during differentiation of myelin-specific T cells and in vivo administration of a T-bet-specific antisense oligonucleotide or siRNA inhibited disease. T-bet was shown to bind the IFNgamma and STAT1 promoters, but did not regulate the IL-12/STAT4 pathway. Since T-bet regulates IFNgamma production in CD4(+) T cells, but to a lesser extent in most other IFNgamma-producing cells, T-bet may be a target for therapeutics for Th1-mediated diseases.